The Visceral Larva Migrans Project is a comprehensive investigation which will determine for the first time the prevalence and pathogenicity of this condition in children. The host and environmental factors which influence the acquisition of the infection and the expression of clinical disease will also be defined. Screening of 8,000 sera from the Lead Poisoning Control Program by the Enzyme-linked Immuno-Sorbent Assay for antibodies to the second larval stage of Toxocara canis, the canine roundworm, will produce an estimated 3.5 percent positivity rate. These 280 positive children and 280 matched controls are then given detailed home questionnaires and clinic examinations. The questionnaire elicits demographic data, information on the subject's play habits and play areas, pet ownership and other animal contact, medical history and parental assessment of how the child functions. An objective appraisal of the interior and exterior home environment is also made. At the clinic sessions, a pediatric physical examination, an ophthalmologic examination, a developmental screening and further blood testing are performed blind on every subject. Referrals are made for all children with positive findings. This comprehensive investigation will not only be the definitive study of Visceral Larva Migrans of children in an urban environment but also reveal valuable insights on pica-related conditions, urban zoonotic conditions, and chronic manifestations of infectious diseases.